Server Side encryption slightly slows down performance when reading data from S3, both
in the reading of data during the execution of a query, and in scanning the files prior to
the actual scheduling of work.

Amazon throttles
reads and writes of S3-SSE data, which results in a significantly lower
throughput than normal S3 IO requests. The default rate, 600 requests/minute, means that
at most ten objects per second can be read or written using SSE-KMS per second — across an
entire hadoop cluster (or indeed, the entire customer account). The default limits may be
suitable during development — but in large scale production applications the limits may
rapidly be reached. Contact Amazon to increase capacity.